The present invention relates generally to plastic manufacturing processes, and more particularly, to methods and systems for thermal molding of plastic.
Manufacturing process for plastic products typically includes heating various forms of plastic (e.g., pellets, powders, sheets, etc.) and forming the plastic into the desired shape. Two very common forms of plastic molding are rotational molding and vacuum molding.
Rotational molding includes a hollow mold that can rotate in all three axis (X, Y, Z axis). The hollow mold is typically formed from a metal or similarly heat-conductive material. A quantity of plastic powder is placed inside the hollow mold. The hollow mold is then moved into an oven where the heat source substantially surrounds the hollow mold. The hollow mold is then rotated and heated in the oven.
As the hollow mold is rotated and heated in the oven, the plastic powder continually falls to the bottom of the inner surface of the hollow mold. The heated hollow mold heats the plastic powder on the bottom inner layer of the hollow mold. The melted plastic powder bonds together (e.g., sinters) to form a complete plastic layer in the bottom inner surface of the hollow mold. Continually rotating the mold forms a plastic layer on all inner surfaces of the hollow mold.
The hollow mold can be removed from the oven once the complete plastic layer is formed on the inner surface of the hollow mold. The hollow mold is then allowed to cool and then opened and the molded plastic product removed from the hollow mold.
Typical products formed in a rotational molding system are tanks, boats, shipping containers and other shapes.
Vacuum molding includes a frame for supporting a sheet of rigid plastic over a positive (raised or convex) or a negative (sunken or concave) shaped mold. A heat source is directed at the plastic sheet and a vacuum is applied to the area around and in some instances inside the mold, softening the plastic sheet and making it flexible. The vacuum draws the heated plastic sheet down onto or into the mold to form the desired shape. Then the heat source is removed and the molded plastic sheet is allowed to cool and become ridged again. Then the vacuum is removed and the molded plastic sheet can be removed from the mold.
Typical products formed in a vacuum molding system are boat hulls, showers, shipping trays, and equipment covers.
In both rotational molding systems and vacuum molding systems, the energy cost for the heat portion of the manufacturing process is an ever larger portion of the end product cost. In view of the foregoing, there is a need for lower cost energy sources for both rotational molding systems and vacuum molding systems.